Aim: Increased plasma low-density lipoprotein cholesterol (LDL-C) concentrations have been shown to be one of the major risk factors for cardiovascular disease (CVD). Clinical evidence also indicates that small dense LDL (sd-LDL) particles are more atherogenic than large buoyant LDL particles. Because there was no easy assay to measure the amount of sd-LDL-C, few studies have addressed the association between sd-LDL-C and CVD. In this study, we hypothesized that higher sd-LDL-C is associated with increased risk for CVD. To this end, we examined the association between sd-LDL-C and CVD in Japanese by using a new kit to measure sd-LDL-C. Methods: We studied 2034 Japanese individuals (30 to 79 years old without stroke or coronary heart disease (CHD)) in the Suita Study, who completed measurement of direct LDL-C and sd-LDL-C by a kit based on the precipitation method with filtration, and then followed for 11.7 years on average. We calculated the Cox proportional adjusted hazard ratios (HRs) of LDL-C, sd-LDL-C, and sd-LDL-C/LDL-C ratio quartiles for incident CAD, stroke, and CVD (CHD + stroke) adjusting for age, sex, body mass index, diabetes, blood pressure category (defined on the basis of the ESH-ESC 2007 criteria), smoking and drinking at baseline. Results: The mean age of this cohort was 59.3 years old and 52.4% was women. The HR of the 4th quartile of sd-LDL-C for the development of CAD was 3.35 (95% confidence intervals: 1.38 to 8.13), which was higher than that in the analysis using LDL-C quartiles. In multivariable adjustment, the HR of the 4th quartile was almost similar. When we used the quartiles of sd-LDL/LDL ratio, increased sd-LDL/LDL ratio was associated with the incidence of CVD, CAD, and stroke. Sex-specific analysis showed that the association of sd-LDL-C with CAD and CVD was statistically significant in men, but not in women. Conclusions: We demonstrated that increased levels of sd-LDL-C are significantly associated with the development of CVD. Our data indicate that sd-LDL-C is a better risk factor for CVD than LDL-C for risk assessment.